Air turbine starters are known in the aviation field, and are commonly used to start propulsion turbine engines of modern aircraft. A persistent problem with high speed sprag-type overrunning clutches of the type used in air turbine starters is wear to the clutch caused by overrunning of the clutch in operation. Such overrunning occurs continuously during operation of a turbine engine, and particularly results in wear of the sprag members of the clutch. Consequently, one or more of the worn sprags may be forced over center during torque transmission through the clutch. Once over center, these sprags will possibly cause the clutch to transmit torque in the direction which should result in overrunning of the clutch. Were the clutch allowed to transmit reverse torque instead of overrunning, the turbine engine would drive the air turbine starter to a high and destructive speed. In order to prevent such destructive back driving of the air turbine starter by the turbine engine, a decoupler mechanism is conventionally provided in the power train between the starter and engine.
Unfortunately all presently known decoupler devices suffer from one or more of several shortcomings. That is, the conventional decoupler mechanisms may be overly large or complex in their construction, they may not be reliable in their operation, some may undesirably reset automatically to a torque transmitting condition after they are tripped by a reverse torque, others may require extensive time consuming disassembly to reset after being tripped by a reverse torque incident.
In view of the above, it is recognized in the pertinent art that an improved decoupler device is needed for use with air turbine starters. The decoupler device should be comparatively small, simple, inexpensive, and rugged in its construction, it should be precise and reliable in its operation, it should not undesirably reengage after being tripped, and it should not require extensive or time consuming effort to reset the device after it is tripped by a reverse torque incident.